Find the most frequent element in .
Wavelet trees don't directly support this, but can help: Approach: Candidate testing Use other techniques (random sampling, heavy hitters) to find candidates, then verify with wavelet tree frequency queries. Approach: Small alphabet If is small, check frequency of each value in .
Approach: Mo's algorithm + frequency tracking For offline queries, Mo's algorithm with frequency map works in .
Mode queries are harder than quantile queries. No known solution exists for arbitrary ranges.